Lecture 22: GUI Applications CS 1110 Introduction to Computing - - PowerPoint PPT Presentation

Lecture 22: GUI Applications

CS 1110 Introduction to Computing Using Python

[E. Andersen, A. Bracy, D. Gries, L. Lee, S. Marschner, C. Van Loan, W. White]

http://www.cs.cornell.edu/courses/cs1110/2019sp

Relevant modules (see schedule page)

• animation.py
• arrows.py
• pyro.py
• state.py
• subcontroller.py
• game2d.zip (unzip)

Try them out! >>> python arrows.py

Update display/view No change to objects Check for user input Process user input Update the objects

A Standard GUI Application

Animates the application, like a movie

while program_is_running: # Get keyboard info ß Handled by OS/GUI libraries # Your code goes here # Draw stuff to screen ß Handled by OS/GUI libraries application.update() ß Custom application class

Example: Animation

class Animation(game2d.GameApp): """App to animate an ellipse in a circle.""" def start(self): """Initializes the game loop.""" … def update(self,dt): """Changes the ellipse position.""" … def draw(self): """Draws the ellipse""" … See animation.py Loop initialization Do NOT use __init__ Loop body Use method draw() defined in GObject

Parent class that does hard stuff

Does update() respond to the user?

A) Yes, any key changes the animation B) Yes, certain keys select certain animations C) No D) I don't know

def update(self,dt): """ Animates the ellipse. Parameter dt: The time since the last animation frame. Precondition: dt is a float. """ # Change the angle self.angle = self.angle+ANIMATION_STEP % (2*math.pi) pos=self._polar_to_coord(ANIMATION_RADIUS,self.angle) self.ellipse.x = pos[0] self.ellipse.y = pos[1]

See animation.py

Does update() respond to the user?

A) Yes, any key changes the animation B) Yes, certain keys select certain animations C) No D) I don't know

See state.py

Changing the Loop Activity

• State: Current loop activity

§ Playing game vs. pausing § Ball countdown vs. serve

• Add an attribute state

§ Method update() checks state § Executes correct helper

• How do we store state?

§ State is an enumeration;

• ne of several fixed values

§ Implemented as an int § Global constants are values

State STATE_CIRCLE State STATE_HORIZONTAL See state.py State STATE_VERTICAL

Need rules for when we switch states

• Attribute key_count in GInput

§ How many keys are pressed? § 0, 1, 2, … § curr_keys = self.input.key_count

• Is this a new key press?

§ Need current curr_keys, and key count from last time: lastkeys

change = curr_keys > 0 and self.lastkeys == 0

• When we're done, curr_keys becomes the new lastkeys

self.lastkeys = curr_keys

See

_determineState(self):

in state.py

Designing Complex Applications

• Applications can become

extremely complex

§ Large classes doing a lot § Many states & invariants § Specification unreadable

• Idea: Break application

up into several classes

§ Start with a “main” class § Other classes have roles § Main class delegates work

MainApp Animation

See subcontroller.py § Processes input § Determines state § Animates (only) Calls the methods of

• Pattern: reusable solution to a common problem

§ Template, not a single program § Tells you how to design your code § Made by someone who ran into problem first

• In many cases, a pattern gives you the interface

§ List of headers for non-hidden methods § Specification for non-hidden methods § Only thing missing is the implementation

How to Break Up: Software Patterns

Just like this course!

Model

• Defines and

manages the data

• Responds to the

controller requests

View

• Displays the model

to the app user

• Provides user input

to the controller

Controller

• Updates model in

response to events

• Updates view with

model changes

Model-View-Controller Pattern

Calls the methods or functions of Division can apply to classes

• r modules

Wave & Invaders Classes Ship, Alien & Bolt Classes draw() methods

Model Subclasses of GObject

• GEllipse, GImage, …
• Often more than one

View Class GView, GInput

• Do not subclass!
• Part of GameApp

Controller

Subclass of GameApp

Model-View-Controller in CS 1110

Classes in game2d Method draw in GObject Attribute view (inherited) Other attributes (defined by you)

Neglected for most

• f this lecture

Models in Assignment 7

• Often subclass of GObject

§ Has built-in draw method § See documentation in A7

• Includes groups of models

§ Example: rockets in pyro.py § Each rocket is a model § But so is the entire list! § update() will change both

• A7: Several model classes

§ Ship to animate the player § Alien to represent an alien

See pyro.py rocket sparks